ortho

Question 1

ortho vs electron penumbra

Answer 1

can use smaller margins in ortho - 5 to 7 mm instead of 1 cm in electrons

Question 2

ortho vs electrons shielding

Answer 2

-ortho uses thinner shielding because it takes advantage of PE effect. Cover with wax to protect against photoelectrons
-for electrons, need thicker shielding. Also cover with wax or paint to protect skin against metal

Question 3

cutout factors in ortho

Answer 3

mresure with PP chamber - output with cutout factor on water surface vs reference cone on water surface

-At Halifax, computer program calculates an equivalent circle from the cutout and estimates a cutout factor (previously validated with measurements)

Question 4

IS in ortho

Answer 4

-IS same for 30 cm cones, but different for 50 cm cones
-paper showed that if you use 35 or 36 cm SSD for 50 cm cones, your error is within 2 %

Question 5

Ortho: lead thickness for <3% transmission:

Answer 5

100 kV: 1 mm
180 kV: 2 mm
250 kV: 3 mm
300 kV: 4 mm

Question 6

SRS OAR constraints per TG101

Answer 6

optic pathway < 0.2 cc 8 Gy, Dmax < 10 Gy
cochlea Dmax < 9 Gy
brainstem < 0.5 cc 10 Gy, Dmax < 15 Gy
spinal cord < 0.35 cc 10 Gy, Dmax < 14 Gy
cauda equina Dmax < 15 Gy
esophagus Dmax< 15 Gy